Fix monitoring thread when refresh period is -1

Change-Id: Ib26177052e6c7daa2ec9e92e1532cc8dd985493a
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/Dockerfile b/Dockerfile
index 27ab273..ea19e3d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -41,5 +41,5 @@
         python3-pip \
         tox
 
-ENV LC_ALL C.UTF-8
-ENV LANG C.UTF-8
+ENV LC_ALL=C.UTF-8
+ENV LANG=C.UTF-8